The present invention relates to an underwater acoustic wave transmitting and receiving unit in which a plate-shaped resonator made of compound piezoelectric material is sealed in a rubber casing which is filled with an insulating liquid matching the surrounding water in acoustic impedance.
A polarized lead titanium zirconate compound is extensively employed as a piezoelectric resonator. If such a resonator is implemented as a plate-shaped resonator in a underwater acoustic wave transmitting and receiving unit, the resonator is well suited for transmitting acoustic waves. However, the resonator is not suitable for receiving waves because the waves are greatly reflected by the surface of the resonator.